EP 0 261 721 A3 discloses a hydraulically or alternatively pneumatically driven actuator of the before mentioned kind which comprises an inner substantially tubular expansion chamber of an elastic and resiliently deformable material which receives a substantially radially outward directed deformation under an inner pressure of the expansion chamber as imparted by an admission of fluid to the expansion chamber. This deformation of the expansion chamber is limited by an outer power transmission envelope which surrounds the expansion chamber and comprises a flexible but non-stretchable fiber material which is anchored at axial ends of the expansion chamber. When the expansion chamber is expanded in a radially outward direction under the inner fluid pressure the non-stretchable fiber material of the outer power transmission envelope then causes oppositely directed forces at the axial ends of the expansion chamber which are transmitted into axial tension forces.
With this known actuator the fiber material comprises monofilaments or multifilaments which are bundled as strings or as strands. These bundled monofilaments or multifilaments are combined for forming a network in which they are extending with opposite spirals under an inclination angle of about 50.degree. to 80.degree. in respect to the longitudinal axis of the expansion chamber. The network allows a relative angular displacement of the filaments at their crossings when the expansion chamber is radially expanded. Since the network is fixedly connected with tie rod members at axial ends of the expansion chamber which are arranged for the transmission of axial tension forces, this will result in an irregular conversion of the fluid energy into such mechanical forces.